Ink-jet recording device

ABSTRACT

The ink-jet recording device includes an image forming section where an active energy ray-curable ink is ejected onto a recording medium to form an image, and an image curing section which includes at least one light irradiation unit having a fluorescent lamp and which cures the ink on the recording medium upon exposure to active energy rays. The fluorescent lamp has a bulb, a reflective film formed on a bulb inner wall and having a first aperture formed on a recording medium side, and a phosphor film formed on the reflective film and the bulb inner wall and having a second aperture formed on the recording medium side. The formulas: β&lt;α, 60°≦α≦150° and 30°≦β≦90° where α represents a first aperture angle of the first aperture and β represents a second aperture angle of the second aperture are satisfied.

The entire contents of all documents cited in this specification areincorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention belongs to the field of ink-jet recording, andmore specifically relates to an ink-jet recording device with which inkthat cures upon exposure to active rays is ejected onto a recordingmedium to form an image thereon.

One method of forming images on a recording medium involves imageformation by ejecting ink droplets from an ink-jet head.

An exemplary device for forming an image with an ink-jet head includesan ink-jet recording device in which an active energy ray-curable inkthat cures upon exposure to active energy rays is ejected from anink-jet head onto a recording medium and is cured by exposure to theactive energy rays. Such ink-jet recording device using an active energyray-curable ink has various advantages: It is anenvironmentally-friendly device; high-speed recording on variousrecording media is possible; what is more, bleeding is not likely tooccur to enable high-definition images to be recorded.

An example of the ink-jet recording device that uses an ink which iscurable upon exposure to active energy rays includes an image recordingdevice described in JP 2004-299296 A which includes recording heads eachhaving nozzles for ejecting light-curable ink therefrom and lightirradiators which are disposed downstream of the corresponding recordingheads in a direction of travel of a recording medium and irradiates theink deposited onto the recording medium with light to cure the depositedink. Each of the light irradiators includes a light source and areflective member on which light from the light source is reflected totravel toward a predetermined light irradiation position on therecording medium. The inside area of the aperture of the reflectivemember which faces the recording medium is irradiated with the lightreflected on the reflective member.

Although not directed to an ink-jet recording device, JP 2006-310084 Adescribes a light-emitting fluorescent lamp including a tubular bulb, alight-reflecting layer which is formed on the inner surface of the bulbalong the tubular bulb axis substantially over the half of thecircumferential surface of the bulb and serves to reflect part ofvisible light, and a phosphor layer which is formed on the bulb innersurface except an aperture formed in the inner surface region of thebulb and on the light-reflecting layer so that the aperture is formed inthe inner surface region of the bulb facing the light-reflecting layer.According to JP 2006-310084 A, it is preferable for the aperture of thereflecting film to be formed so that the angle of aperture from the bulbaxis is 180±20° and for the aperture of the phosphor layer to be formedso that the angle of aperture from the bulb axis is in the range of 20°to 120°.

SUMMARY OF THE INVENTION

Prints can be produced at a high rate in a so-called single pass ink-jetrecording device in which an elongated recording medium capable ofhigh-speed transport is used, an ink-jet head having an enough width toenable recording on the whole area in the width direction of therecording medium is fixed at an opposed position to the recording medium(or its travel path), and recording is accomplished by passing therecording medium under the ink-jet head only once.

In the case where color printing is carried out with such a single passink-jet recording device, fixed heads whose number corresponds to thenumber of colors are disposed in the direction of travel of therecording medium, and by disposing the light irradiating meansdownstream of the heads for the respective colors as in the ink-jetrecording device described in JP 2004-299296 A, inks of different colorsare prevented from intermingling. However, even if the light irradiatingmeans are disposed downstream of the heads for the respective colors,deposition interference that adjacent dots are merged together on arecording medium or on ink cured after ejection from an ink-jet headdisposed further upstream in the direction of travel of the recordingmedium, may occur to lower the image quality.

In the case of producing a print having an image formed thereon at ahigh rate, a higher irradiation intensity is required to cure ink in ashort period of time.

However, light irradiating means having a high irradiation intensity isexpensive and therefore involves an increased device cost.

The fluorescent lamp described in JP 2006-310084 A that has thelight-reflecting layer is capable of further illuminating the same areathan before being provided with the light-reflecting layer, butsufficient exposure is not achieved when light is irradiated for a shortperiod of time.

In addition, if the irradiation intensity of the light irradiating means(or the fluorescent lamp) or the sensitivity to curing of the ink isincreased in view of the improvement of the productivity, the ink-jethead nozzles are likely to be clogged.

The present invention has been accomplished with a view to solving theabove-mentioned problems of the prior art and an object of the presentinvention is to provide an inexpensive, compact ink-jet recording devicethat is capable of consistently and rapidly producing prints havinghigh-resolution and high-quality images formed therein for an extendedperiod of time and also capable of reducing the maintenance frequency.

In order to achieve the above object, a first aspect of the inventionprovides an ink-jet recording device comprising: transport means fortransporting a recording medium; image forming means which includes atleast one ink-jet head that ejects, based on image signals, inkcontaining at least a colorant and cured by exposure to active energyrays onto the recording medium transported by the transport means andmoved to a position opposed to the at least one ink-jet head; and imagecuring means which includes at least one light irradiation unit having afluorescent lamp from which the active energy rays are emitted, andwhich cures the ink deposited on the recording medium by irradiation ofan image formed on the recording medium with the active energy rays fromthe at least one light irradiation unit, wherein the fluorescent lamphas a bulb, a reflective film formed on a large part of an inner wall ofthe bulb and having a first aperture formed on a side of the recordingmedium, and a phosphor film formed on the reflective film and a part ofthe inner wall of the bulb and having a second aperture formed on theside of the recording medium, and wherein formulas: β<α, 60°≦α≦150° and30°≦β≦90° where α represents a first aperture angle of the firstaperture for the reflective film and β represents a second apertureangle of the second aperture for the phosphor film, are satisfied.

In the ink-jet recording device of the first aspect, the reflective filmpreferably has a transmittance of not more than 10%.

In order to achieve the above object, a second aspect of the inventionprovides an ink-jet recording device comprising: transport means fortransporting a recording medium; image forming means which includes atleast one ink-jet head that ejects, based on image signals, inkcontaining at least a colorant and cured by exposure to active energyrays onto the recording medium transported by the transport means andmoved to a position opposed to the at least one ink-jet head; and imagecuring means which includes at least one light irradiation unit having afluorescent lamp from which the active energy rays are emitted, andwhich cures the ink deposited on the recording medium by irradiation ofan image formed on the recording medium with the active energy rays fromthe at least one light irradiation unit, wherein the fluorescent lamphas a bulb, a reflective film formed on a large part of an inner wall ofthe bulb and having a first aperture formed on a side of the recordingmedium, and a phosphor film formed on the reflective film and a part ofthe inner wall of the bulb and having a second aperture formed on theside of the recording medium, and wherein the reflective film has atransmittance of not more than 10%.

In the ink-jet recording devices of the first and second aspects, thefirst aperture of the reflective film and the second aperture of thephosphor film are preferably symmetric with respect to a axial planeconnecting a centre of the fluorescent lamp with the recording medium.

It is preferable for the at least one light irradiation unit to furtherinclude a housing which is disposed so as to surround the fluorescentlamp and has an opening formed on the side of the recording medium.

The at least one ink-jet head is preferably of a full-line type in whichthe at least one ink-jet head has a length in a direction perpendicularto a direction of travel of the recording medium which is larger than awidth of the recording medium and ink droplets can be ejected over awhole area of the recording medium in the direction perpendicular to thedirection of travel of the recording medium.

Preferably, the at least one ink-jet head of the image forming meanscomprises at least two ink-jet heads from which inks of different colorsare ejected, and the at least one light irradiation unit of the imagecuring means comprises at least one light irradiator disposed betweenadjacent ink-jet heads of the at least two ink-jet heads in a directionof travel of the recording medium and a final light irradiator whichirradiates the active energy rays onto images formed on the recordingmedium.

The final light irradiator is preferably configured as in the at leastone light irradiator.

The final light irradiator preferably comprises a metal halide lamp or ahigh-pressure mercury vapor lamp.

Preferably, the at least one light irradiator disposed between theadjacent ink-jet heads of the at least two ink-jet heads semi-cures inkconstituting an image formed by an ink-jet head located upstream of theat least one light irradiator in the direction of travel of therecording medium, and the final light irradiator cures inks of theimages formed on the recording medium.

It is preferable for the ink-jet recording device to further compriseundercoating liquid applying means which is disposed upstream from theimage forming means in a direction of travel of the recording mediumtransported by the transport means and which applies to the recordingmedium undercoating liquid that cures upon exposure to the active energyrays; and undercoating liquid semi-curing means which is disposeddownstream of the undercoating liquid applying means in the direction oftravel of the recording medium and which includes a light irradiationunit, the undercoating liquid applied onto the recording medium beingirradiated with active energy rays from the light irradiation unit tosemi-cure the undercoating liquid applied on the recording medium.

According to the invention, by providing the fluorescent lamp with areflective film and a phosphor film each having an aperture formedtherein and by forming the apertures so as to have such shapes that theaperture angles satisfy the above-defined ranges or setting thetransmittance of the reflective film to not more than 10%, the recordingmedium side can be irradiated with high intensity light while reducingthe intensity of light traveling in other directions even in the casewhere the fluorescent lamp used is inexpensive.

An image can be thus cured to a desired state even in the case where therecording medium travels at a high speed. Light is prevented fromreaching the ink-jet head to cause nozzle clogging or this phenomenon issuppressed to enable the maintenance frequency to be reduced.

As a result, prints having high-resolution and high-quality imagesformed therein can be rapidly produced for a long time in a consistentmanner. Use of the fluorescent lamp enables the light irradiation unitand hence the device to be manufactured at a low cost. Provision of thereflective film within the bulb of the fluorescent lamp enables thelight irradiation unit and hence the image curing means to be downsizedbecause it is not necessary to provide space for disposing a reflectivemember such as a reflector on the circumference of the fluorescent lamp.

A higher-resolution and higher-quality image can be formed by applyingthe undercoating liquid onto the recording medium and semi-curing theapplied undercoating liquid.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a front view schematically showing the structure of anembodiment of an ink-jet recording device according to the invention;

FIG. 2A is a longitudinal sectional view schematically showing thestructure of an exemplary fluorescent lamp used in UV irradiation unitsof the ink-jet recording device shown in FIG. 1;

FIG. 2B is a sectional view, taken along the line B-B, of thefluorescent lamp shown in FIG. 2A;

FIG. 3 is a schematic sectional view of a recording medium where inkdroplets have been deposited onto a semi-cured undercoating liquid;

FIGS. 4A and 4B are schematic sectional views of recording media whereink droplets have been deposited onto an undercoating liquid that is inan uncured state;

FIG. 4C is a schematic sectional view of a recording medium where inkdroplets have been deposited onto an undercoating liquid that is in acompletely cured state;

FIG. 5 is a schematic sectional view of a recording medium where inkdroplets have been deposited onto a semi-cured ink liquid;

FIGS. 6A and 6B are schematic sectional views of recording media whereink droplets have been deposited onto an ink liquid that is in anuncured state;

FIG. 6C is a schematic sectional view of a recording medium where inkdroplets have been deposited onto an ink liquid that is in a completelycured state;

FIGS. 7A to 7D are schematic diagrams showing steps in the formation ofan image on a recording medium;

FIG. 8 is a front view showing, in simplified form, an embodiment of adigital label printer which uses the ink-jet recording device of theinvention; and

FIG. 9 is a longitudinal sectional view of a recording medium forprinting labels such as may be used in the digital label printer shownin FIG. 8.

DETAILED DESCRIPTION OF THE INVENTION

The ink-jet recording device according to the present invention isdescribed more fully below based on the embodiments shown in theaccompanying diagrams.

FIG. 1 is a front view schematically showing the structure of anembodiment of an ink-jet recording device according to the invention;FIG. 2A is a longitudinal sectional view schematically showing thestructure of an exemplary fluorescent lamp used in UV irradiation unitsof the ink-jet recording device shown in FIG. 1; and FIG. 2B is asectional view, taken along the line B-B, of the fluorescent lamp shownin FIG. 2A.

In the embodiments described below, active light-curable ink-jetrecording devices which use an ultraviolet light-curable ink (UV-curableink) as the active light-curable ink (also referred to as “active energyray-curable ink”) that cures under irradiation with active light (alsoreferred to as “active energy rays”) are described below. However, theinvention is not limited to this and may apply to ink-jet recordingdevices in which various types of active light-curable inks are used.Examples of the active light that may be used in the invention includeUV light and visible light.

As shown in FIG. 1, an ink-jet recording device 10 has a transportsection 12 which transports a recording medium P, an undercoat formingsection 13 which coats an undercoating liquid onto the recording mediumP, an undercoating liquid semi-curing section 14 which semi-cures theundercoating liquid that has been coated onto the recording medium P, animage recording section 16 which records an image on the recordingmedium P, an image fixing section 18 which fixes the image recorded onthe recording medium P, and a control unit 20 which controls theejection of ink droplets from the image recording section 16.

An input unit 22 is connected to the control unit 20 of the ink-jetrecording device 10. The input unit 22 may be an image reading unit suchas a scanner or any of various types of devices which transmit imagedata, including image processing devices such as a personal computer.Any of various connection methods, whether wired or wireless, may beused to connect the input unit 22 and the control unit 20.

The transport section 12, which has a feed roll 30, a transport roll 32,a transport roller pair 34 and a recovery roll 36, feeds, transports andrecovers the recording medium P.

The feed roll 30 has a web-type recording medium P wrapped thereon inthe form of a roll, and feeds the recording medium P.

The transport roll 32 is disposed on the downstream side of the feedroll 30 in the direction of travel of the recording medium P, andtransports the recording medium P that has been let out from the feedroll 30 to the downstream side in the direction of travel.

The transport roller pair 34 is a pair of rollers which are disposed onthe downstream side of the transport roll 32 in the travel path of therecording medium P and which grip therebetween the recording medium Pthat has passed around the transport roll 32 and transport it to thedownstream side in the direction of travel.

The recovery roll 36 is disposed the furthest downstream on the travelpath of the recording medium P. The recovery roll 36 takes up therecording medium P which has been fed from the feed roll 30, has beentransported by the transport roll 32 and the transport roller pair 34,and has passed through positions facing the subsequently describedundercoat forming section 13, undercoating liquid semi-curing section14, image recording section 16 and image fixing section 18.

Here, the transport roll 32, the transport roller pair 34 and therecovery roll 36 are connected to drive units (not shown) and rotated bythe drive units.

Here, the transport roll 32 is disposed above the feed roll 30 in avertical direction, and at a position farther from the recovery roll 36than from the feed roll 30 in a horizontal direction. Moreover, thetransport roll 32, the transport roller pair 34 and the recovery roll 36are disposed linearly in a direction parallel to the horizontaldirection.

The transport section 12 is configured as described above and transportsthe recording medium P let out from the feed roll 30 upward whileinclined at a given angle with respect to the vertical direction towardthe side away from the recovery roll 36, following which the transportsection 12 changes the direction of travel of the recording medium P atthe transport roll 32 so that, after the recording medium P has passedthe transport roll 32, it is transported horizontally toward therecovery roll 36.

In other words, after the recording medium P has been let out from thefeed roll 30, it is moved in an upwardly inclined direction with thesurface on which images are to be recorded facing downward. Afterpassing around the transport roll 32, the recording medium P is moved ina horizontal direction with the surface on which images are to berecorded facing upward.

The undercoat forming section 13 is situated between the feed roll 30and the transport roll 32; that is, on the downstream side of the feedroll 30 and on the upstream side of the transport roll 32 in thedirection of travel of the recording medium P.

The undercoat forming section 13 has a coating roll 60 for coating anundercoating liquid onto the recording medium P, a drive unit 62 whichdrives the coating roll 60, a reservoir 64 which supplies theundercoating liquid to the coating roll 60, a scraper roll 66 whichadjusts the amount of undercoating liquid picked up by the coating roll60, a scraper roll drive unit 67 which drives the scraper roll 66(hereinafter referred to simply as the “drive unit 67”) and apositioning unit 68 which supports the recording medium P so that therecording medium P assumes a predetermined position relative to thecoating roll 60.

The coating roll 60 is disposed between the feed roll 30 and thetransport roll 32 in the travel path of the recording medium P so as tobe in contact with the surface of the recording medium P which istraveling between the feel roll 30 and the transport roll 32 and onwhich images are to be formed. That is, the coating roll 60 is incontact with the downwardly facing surface of the recording medium Pbeing transported from the feed roll 30 to the transport roll 32.

The coating roll 60, which is a roll that is longer than the width ofthe recording medium P, is a so-called gravure roller on the surface(peripheral face) of which recessed features are formed at fixed, i.e.,uniform, intervals. Here, the shapes of the recessed features formed onthe coating roll 60 are not subject to any particular limitation. Any ofvarious shapes may be used, including round, rectangular, polygonal orstar-like shapes. Alternatively, the recessed features may be formed asgrooves extending over the entire circumference of the coating roll.Since the amount of undercoating liquid held on the surface of thecoating roll 60 can be made constant, the coating roll 60 preferably hassuch a shape that recessed features are formed on its surface at fixedintervals. However, this is not the sole case of the present inventionbut a roll having no recessed features formed thereon may also be used.

The drive unit 62 is a drive mechanism including a motor, and gearswhich transmit rotation of the motor to the coating roll 60 and rotatesthe coating roll 60. However, the drive unit 62 is not limited to thisembodiment. Any of various other drive mechanisms may instead be used torotate the coating roll 60, including pulley driving, belt driving anddirect driving.

As indicated by an arrow in FIG. 1, the drive unit 62 causes the coatingroll 60 to rotate in the direction opposite to the direction of travelof the recording medium P at the portion of contact therebetween (i.e.,in the clockwise direction in FIG. 1).

The reservoir 64 has a dish-like shape open at the top, and holds in theinterior thereof the undercoating liquid. The reservoir 64 is disposedunderneath and adjacent to the coating roll 60, such that a portion ofthe coating roll 60 is immersed in the undercoating liquid held withinthe reservoir 64. When necessary, the undercoating liquid is fed to thereservoir 64 from a feed tank (not shown).

The scraper roll 66 is a roll having substantially the same axial lengthas the coating roll 60. The scraper roll 66 is rotatably disposed in astate in which it is in contact with the surface of the coating roll 60.More specifically, the scraper roll 66 is disposed downstream of thereservoir 64 and upstream of the recording medium P in the rotationaldirection of the coating roll 60.

The scraper roll 66 scrapes off that portion of the undercoating liquidpicked up by the coating roll 60 when immersed in the reservoir 64 whichis not needed, thereby setting the quantity of undercoating liquidadhering to the coating roll 60 to a fixed amount. In this embodiment,except for the undercoating liquid retained in the recessed featuresformed on the surface of the coating roll 60, the scraper roll 66scrapes off undercoating liquid adhering to other portions of thecoating roll 60 so that the portion of the coating roll 60 which comesin contact with the recording medium P has the undercoating liquidsubstantially only held in the recessed features.

The scraper roll 66 scrapes off undercoating liquid excessively adheringto the surface of the coating roll 60 (i.e., surplus undercoatingliquid) to make the amount of undercoating liquid adhering to thesurface of the coating roll 60 constant, thus enabling the coating layerto be more uniformly formed on the recording medium.

As shown by an arrow in FIG. 1, the drive unit 67 rotates the scraperroll 66 in the opposite direction from the rotational direction of thecoating roll 60 so that the direction of movement of the scraper roll 66surface and the direction of movement of the coating roll 60 at theposition of contact between the scraper roll 66 and the coating roll 60are the same (in the counterclockwise direction in FIG. 1). As in thedrive unit 62, various drive mechanisms may be used to rotate the roll,including gear driving, pulley driving, belt driving and direct driving.The drive unit 67 rotates the scraper roll 66 in the opposite directionfrom the rotational direction of the coating roll 60 to prevent abrasionof the scraper roll 66 and the coating roll 60, thus enabling theirreplacement frequency to be reduced while enhancing the devicedurability.

Since the device can have a higher durability, undercoating liquidexcessively adhering to the coating roll 60 is preferably scraped off bya scraper roll as in the embodiment under consideration. However, thisis not the sole case of the present invention but use may be made of amethod using a blade in which the blade is brought into contact with thecoating roll 60 to scrape off undercoating liquid excessively adheringto the coating roll 60.

The positioning unit 68 has a first positioning roll 70 and a secondpositioning roll 72, and supports the recording medium P in such a wayas to ensure that the recording medium P comes into contact with thecoating roll 60 at a specified position.

The first and second positioning rolls 70 and 72 are each situated onthe opposite side of the recording medium P from the coating roll 60and, in the direction of travel of the recording medium P, on eitherside of the coating roll 60; that is, one is situated on the upstreamside, and the other is situated on the downstream side, of the coatingroll 60. These first and second positioning rolls 70 and 72 support therecording medium P from the side of the recording medium P opposite tothe side on which images are to be formed (i.e., the side to be coatedwith undercoating liquid).

It is preferable to provide a positioning mechanism for fixing themutual positions of the coating roll 60, the first positioning roll 70and the second positioning roll 72 in the undercoat forming section 13.By thus providing the positioning mechanism, departures from the correctpositional relationships between the coating roll 60 and the positioningrolls 70 and 72 can be prevented from occurring.

Any positioning mechanism may be used as long as it is configured suchthat members which individually support the coating roll 60 and thefirst and second positioning rolls 70 and 72 are placed in mutualcontact. For example, use may be made of a mechanism in which thebearings of the respective members are placed in mutual contact, and amechanism in which fixing members which fix in place the bearings areplaced in mutual contact.

In the foregoing arrangement of the undercoat forming section 13, thedrive unit 62 causes the coating roll 60 to rotate in the directionopposite to the direction of travel of the recording medium P. Afterbeing immersed in the undercoating liquid which has accumulated in thereservoir 64, the surface of the rotating coating roll 60 comes intocontact with the scraper roll 66, thereby setting the amount ofundercoating liquid retained on the surface to a fixed amount, thencomes into contact with the recording medium P, thereby coating theundercoating liquid onto the recording medium P. By thus rotating thecoating roll 60 in the direction opposite to the direction of travel ofthe recording medium P and coating the undercoating liquid onto therecording medium P, a layer of undercoating liquid (referred to below asthe “undercoat”) that has been smoothened and has a good, even, coatingsurface state can be formed on the recording medium P. The coating roll60 that came into contact with the recording medium P is further rotatedto be immersed again in the coating liquid within the reservoir 64.

Next, the undercoating liquid semi-curing section 14 is described.

The undercoating liquid semi-curing section 14 includes a UV irradiationunit and is disposed so as to face the recording medium P.

The UV irradiation unit has a fluorescent lamp emitting UV light, ahousing which is disposed so as to surround the fluorescent lamp, has anopening formed on the recording medium P side and reflects light emittedfrom the fluorescent lamp, and a cooling mechanism which is disposed inthe housing and blows air to the fluorescent lamp for its cooling, andirradiates UV light onto the recording medium P. The UV irradiation unitwill be described later in detail in connection with the image fixingsection 18.

The undercoating liquid semi-curing section 14 exposes to UV light theentire width of the recording medium P which has been coated on thesurface with the undercoating liquid and passes through a positionopposed thereto, thereby rendering the undercoating liquid coated ontothe surface of the recording medium P into a semi-cured state.Semi-curing of the undercoating liquid will be described later infurther detail.

Next, the image recording section 16 in which ink droplets are ejectedonto the recording medium to record an image and the image fixingsection 18 in which the image formed on the recording medium in theimage recording section 16 is cured to fix it on the recording mediumare described.

The image recording section 16 has a recording head unit 46 and inktanks 50X, 50Y, 50C, 50M and 50K.

The recording head unit 46 has recording heads 48X, 48Y, 48C, 48M and48K.

The recording heads 48X, 48Y, 48C, 48M and 48K are arranged in thisorder from the upstream side to the downstream side in the direction oftravel of the recording medium P. Moreover, in the recording heads 48X,48Y, 48C, 48M and 48K, the tips of the respective ink ejection portionsare disposed so as to face the path of travel of the recording medium P;that is, so as to face the recording medium P which is transported overthe travel path by the transport section 12 (also referred to below assimply “facing the recording medium P”).

The recording heads 48X, 48Y, 48C, 48M and 48K are full-line,piezoelectric ink-jet heads in which a large number of orifices(nozzles, ink ejection portions) are arranged at fixed intervalsthroughout in a direction perpendicular to the direction of travel ofthe recording medium P, that is, over the entire width of the recordingmedium P. These recording heads are connected to the subsequentlydescribed control unit 20 and the ink tanks 50X, 50Y, 50C, 50M and 50K.The amount of ink droplets ejected by the recording heads 48X, 48Y, 48C,48M and 48K and the ejection timing of the droplets are controlled bythe control unit 20. The recording heads 48X, 48Y, 48C, 48M and 48Keject inks of special color (X), yellow (Y), cyan (C), magenta (M) andblack (K).

A color image can be formed on the recording medium P by ejecting inksof various colors—special color (X), yellow (Y), cyan (C), magenta (M)and black (K)—from the respective recording heads 48X, 48Y, 48C, 48M and48K toward the recording medium P while at the same time having thetransport section 12 transport the recording medium P.

In the present embodiment, the recording heads are piezoelectric (piezo)elements. However, the invention is not limited in this regard. Any ofvarious types of systems may be used in place of a piezo system, such asa thermal jet system which uses a heating element such as a heater toheat the ink and generate bubbles. In this latter system, the pressureof the bubbles propels the droplets of ink.

Any of various inks, such as white, orange, violet or green ink may beused as the special colored ink ejected from the recording head 48X. Thenumber of inks ejected from the recording head 48X is not limited to onebut a plurality of inks may be ejected therefrom. As for the order inwhich the recording heads 48X, 48Y, 48C, 48M and 48K are arranged, thisembodiment is not the sole case but the recording heads may be arrangedin various orders.

The inks ejected from the recording heads in the present embodiment areUV-curable inks.

The ink tanks 50X, 50Y, 50C, 50M and 50K are provided for the recordingheads 48X, 48Y, 48C, 48M and 48K. The respective ink tanks 50X, 50Y,50C, 50M and 50K store inks of various colors for the recording heads,and supplies the stored inks to the corresponding recording heads 48X,48Y, 48C, 48M and 48K.

In addition, a tabular platen 56 is disposed at a position facing therecording heads 48X, 48Y, 48C, 48M and 48K on the side of the recordingmedium P where images will not be formed.

The platen 56 supports the recording medium P which is transportedthrough positions facing the respective recording heads from the side ofthe recording medium P on which images will not be formed; that is, fromthe opposite side of the recording medium P to that on which therecording head unit 46 is disposed. In this way, the distance betweenthe recording medium P and the respective recording heads can be madeconstant, enabling high-resolution images to be formed on the recordingmedium P.

The shape of the platen 56 is not limited to a flat plate, and may havea raised, curved surface shape on the recording head side. In such acase, the recording heads 48X, 48Y, 48C, 48M and 48K are disposed atfixed distances from the platen.

Then, the image fixing section 18, which has UV irradiation units 52X,52Y, 52C and 52M, and a final UV irradiation unit for curing 54,irradiates UV light onto the image formed on the recording medium P bythe recording head unit 46, thereby semi-curing the image (that is, theinks) with the UV irradiation units 52X, 52Y, 52C and 52M, then curingit with the final UV irradiation unit for curing 54, thus fixing theimage.

The UV irradiation units 52X, 52Y, 52C and 52M are disposed on thedownstream sides of the respective recording heads 48X, 48Y, 48C and 48Malong the travel path of the recording medium P. In addition, the finalUV irradiation unit for curing 54 is disposed on the downstream side ofthe recording head 48K along the travel path of the recording medium P.That is, the final UV irradiation unit for curing 54 is positioned onthe downstream side of the recording head situated the furthestdownstream of all the recording heads along the travel path of therecording medium P.

In other words, as shown in FIG. 1, the respective recording heads 48X,48Y, 48C, 48M and 48K, the respective UV irradiation units 52X, 52Y, 52Cand 52M, and the final UV irradiation unit for curing 54 are disposed inthe following order, from the upstream to the downstream side of thetravel path: recording head 48X, UV irradiation unit 52X, recording head48Y, UV irradiation unit 52Y, recording head 48C, UV irradiation unit52C, recording head 48M, UV irradiation unit 52M, recording head 48K,final UV irradiation unit for curing 54.

Here, the UV irradiation units 52X, 52Y, 52C and 52M and the final UVirradiation unit for curing 54 differ only in the size of the units, thetarget to be irradiated with UV light and the degree of cure.Specifically, the UV irradiation units 52X, 52Y, 52C and 52M semi-curethe images formed by the respective recording heads, whereas the finalUV irradiation unit for curing 54 differs only in that it irradiateshigher intensity light than the other UV irradiation units so as toreliably cure both the undercoating liquid coated onto the recordingmedium P and images of all the respective inks. Because the final UVirradiation unit for curing 54 has the same basic construction as the UVirradiation units 52X, 52Y, 52C and 52M, the description given below forthe UV irradiation unit 52X applies collectively to all of the above UVirradiation units, including the final UV irradiation unit for curing54.

Now, the UV irradiation unit 52X is described with reference to FIGS. 1,2A and 2B.

The UV irradiation unit 52X has a fluorescent lamp 80 emitting UV light,a housing 82 which is disposed so as to surround the fluorescent lamp 80and which has an opening formed on the recording medium P side, and acooling mechanism 84 which is disposed within the housing 82 and whichblows air to the fluorescent lamp 80 for its cooling. The UV irradiationunit 52X is disposed so as to face the travel path of the recordingmedium P.

The fluorescent lamp 80 is a linear light source which emits UV lightand is disposed so that a direction orthogonal to the direction oftravel of the recording medium P is parallel to the axial direction inwhich the fluorescent lamp 80 extends. The fluorescent lamp 80 has alength which is larger than that of the recording medium P in the widthdirection, and is disposed over the entire width of the recording mediumP.

As shown in FIGS. 2A and 2B, the fluorescent lamp 80 has a bulb 86,electrodes 88, a reflective film 90, and a phosphor film 92.

The bulb 86 is a tubular (or cylindrical) member made of a material suchas soda glass or fused silica (sterile glass). Tubes having a length inthe range of from 500 mm to 800 mm may be used for the bulb 86. Tubeshaving diameters of 15.5 mm, 20 mm, 25.5 mm, 28 mm, 32 mm, and 38 mm maybe used for the bulb 86.

The electrodes 88 protrude into the space formed in the bulb 86, haveeach a filament through which electric current flows, and are disposedat both ends of the bulb 86.

The bulb 86 and the electrodes 88 at both ends of the bulb 86 aredisposed so as to hermetically seal the bulb 86, and mercury or othermaterial is sealed within the bulb 86.

The reflective film 90 is made of a light reflective material and isformed on the inner wall surface of the bulb 86.

The phosphor film 92 is made of a phosphor which emits UV light at 280to 400 nm, and is formed on the reflective film 90 and part of the innerwall surface of the bulb 86.

In this way, the fluorescent lamp 80 is of a structure in which the bulb86, the reflective film 90 and the phosphor film 92 are stacked on topof each other from the outside toward the center of the fluorescent lamp80.

In addition, as shown in FIG. 2B, neither the reflective film 90 nor thephosphor film 92 is formed on the bulb 86 on the recording medium P side(on the bottom side in FIG. 2B) and these portions corresponding to thereflective film 90 and the phosphor film 92 are hereinafter referred toas apertures 94 and 96, respectively.

The reflective film 90 and the phosphor film 92 have shapes satisfyingthe conditions: β<α, 60°≦α≦150° and 30°≦β≦90° wherein α represents theaperture angle of the aperture 94 for the reflective film 90 and βrepresents the aperture angle of the aperture 96 for the phosphor film92. The aperture angle as used herein refers to an angle formed betweena first line segment that connects the center of the section of thefluorescent lamp which is orthogonal to the longitudinal direction (i.e.the center of the reflective film 90 or the phosphor film 92 formed onthe circumference of the bulb 86) and a first aperture end, and a secondline segment that connects the center of the section and a secondaperture end.

Since the condition of β<α is satisfied, the fluorescent lamp 80 has, onthe recording medium P side of the bulb 86, a first region where both ofthe reflective film 90 and the phosphor film 92 are not formed on thebulb 86 and a second region where the phosphor film 92 is only formedthereon. In other words, the bulb 86 has the second region where thephosphor film 92 is directly formed on the bulb 86.

The fluorescent lamp 80 has the arrangement as described above. When thefilaments of the electrodes 88 are preheated by application of electriccurrent, electrons are released from emitters having an elevatedtemperature (emitters being coated on the filaments) to collide withmercury atoms sealed within the fluorescent lamp 80. Mercury generatesUV light. Then, upon exposure to the thus generated UV light, thephosphor film 92 emits light at the respective wavelengths. The emittedlight then travels through the aperture 94 toward the recording medium Pdirectly or after having been reflected on the reflective film 90.

The housing 82 is in the shape of a rectangular parallelepiped box andis disposed so as to surround the periphery of the fluorescent lamp 80.The housing 82 has an open surface on the side of the recording mediumP. In other words, the surface of the housing 82 on the recording mediumP side is opened and light emitted from the fluorescent lamp 80 passesthrough the opened surface to strike on the recording medium P.

The cooling mechanism 84 is an air blowing machine such as a cooling fanor an air blower, and is disposed within the housing 82 on the side ofthe fluorescent lamp 80 away from the recording medium P (i.e., on theupper side of the fluorescent lamp 80 in FIG. 1). The cooling mechanism84 blows air toward the fluorescent lamp 80 for its cooling.

The cooling mechanism 84 also has a temperature sensor for detecting thetemperature of the fluorescent lamp 80. The volume of air and the timeof air blowing are adjusted to regulate the amount of cooling therebymaintaining the fluorescent lamp 80 at a constant temperature.

An opening is preferably formed in the housing 82 so that air to beblown from the cooling mechanism 84 to the fluorescent lamp 80 isaspirated through the opening.

The UV irradiation unit 52X is basically configured as described above.

Next, the control unit 20 is connected to the respective recording heads48X, 48Y, 48C, 48M and 48K of the recording head unit 46 and, usingimage data sent from the input unit 22 as the image recording signals,controls ink ejection/non-ejection from the respective recording heads48X, 48Y, 48C, 48M and 48K so as to form images on the recording mediumP.

The ink-jet recording device 10 has the basic layout as described above.

Semi-curing the undercoating liquid and ink is now described.

In the practice of the invention, the term “semi-curing the undercoatingliquid” as used herein signifies partial curing, and refers to theundercoating liquid in a partially cured, i.e., an incompletely cured,state. When the undercoating liquid that has been applied onto therecording medium (base material) P is semi-cured, the degree of curingmay be non-uniform; preferably, the degree of curing proceeds in thedepth direction of the undercoating liquid. In the present embodiment,the undercoating liquid which is semi-cured is an undercoating liquidwhich forms an undercoat.

For example, when a radical-polymerizable undercoating liquid is curedin air or air that is partially flushed with an inert gas, due to theradial polymerization-suppressing effect of oxygen, radicalpolymerization tends to be inhibited at the surface of the undercoatingliquid. As a result, semi-curing is non-uniform, there being a tendencyfor curing to proceed at the interior of the undercoating liquid and tobe delayed at the surface.

In the practice of the invention, by using a radical-photopolymerizableundercoating liquid in the presence of oxygen which tends to inhibitradical polymerization, the undercoating liquid partially photocures,enabling the degree of cure of the undercoating liquid to be higher atthe interior than at the exterior.

Alternatively, in cases where a cationic-polymerizable undercoatingliquid is cured in air containing humidity, because moisture has acationic polymerization-inhibiting effect, there is a tendency forcuring to proceed at the interior of the undercoating liquid and to bedelayed at the surface.

It is likewise possible for the degree of cure in the undercoatingliquid to be made higher at the interior than at the exterior by usingthis cationic-polymerizable undercoating liquid under humid conditionsthat have a cationic polymerization-inhibiting effect so as to inducepartial photocuring.

By thus semi-curing the undercoating liquid and depositing ink dropletson the semi-cured undercoating liquid, technical effects that areadvantageous for the quality of the resulting print can be achieved. Themechanism of action can be confirmed by examining a cross-section of theprint.

The semi-curing of the undercoating liquid (i.e., the undercoat formedof undercoating liquid on the recording medium) is described in detailbelow. As one illustration, high-density areas obtained by depositingabout 12 pL of liquid ink (that is, droplets of ink) on the undercoatingliquid in a semi-cured state having a thickness of about 5 μm that hasbeen provided on a recording medium P are described below.

FIG. 3 is a schematic sectional view of a recording medium where inkdroplets have been deposited onto a semi-cured undercoating liquid.FIGS. 4A and 4B are schematic sectional views of recording media whereink droplets have been deposited onto an undercoating liquid that is inan uncured state, and FIG. 4C is a schematic sectional view of arecording medium where ink droplets have been deposited onto anundercoating liquid that is in a completely cured state.

When the undercoating liquid is semi-cured according to the invention,the degree of cure on the recording medium P side is higher than thedegree of cure at the surface layer. In this case, three features areobservable. That is, as shown in FIG. 3, when ink d is deposited asdroplets on a semi-cured undercoating liquid U, (1) a portion of the inkd emerges at the surface of the undercoating liquid U, (2) a portion ofthe ink d lies within the undercoating liquid U, and (3) theundercoating liquid is present between the bottom side of the ink d andthe recording medium P.

When the ink d is deposited on the undercoating liquid U, if theundercoating liquid U and the ink d satisfy the above states (1), (2)and (3), the undercoating liquid U can be regarded as being in asemi-cured state.

By semi-curing the undercoating liquid U, that is, by curing theundercoating liquid U so that it satisfies above (1), (2) and (3), thedroplets of ink d (i.e., the ink droplets) which have been deposited toa high density mutually connect, forming a film of the ink d (i.e., anink film or ink layer), and thus providing a uniform and high colordensity.

By contrast, when the ink is deposited on the undercoating liquid whichis in an uncured state, either or both of the following occur: all ofthe ink d lies within the undercoating liquid U as shown in FIG. 4A; astate arises where, as shown in FIG. 4B, the undercoating liquid U isnot present below the ink d.

In this case, even when the ink is applied to a high density, the liquiddroplets are mutually independent, causing the color density todecrease.

When the ink is deposited on an undercoating liquid that is completelycured, as shown in FIG. 4C, a state will arise where the ink d does notlie within the undercoating liquid U.

In this case, interference in the deposition of the droplets arises, asa result of which a uniform ink film cannot be formed and a high colorreproducibility cannot be achieved (i.e., this leads to a decrease incolor reproducibility).

Here, when the droplets of ink are applied to a high density, thedroplets are not independent of each other. To form a uniform ink film,and also to suppress the occurrence of deposition interference, thequantity of regions where the undercoating liquid (i.e., the undercoat)is uncured per unit surface area is preferably smaller, and morepreferably substantially smaller, than the maximum quantity of dropletsof ink applied per unit surface area. That is, the relationship betweenthe weight M_(u) (also referred to as M_(undercoating liquid)) ofuncured regions of the undercoat per unit surface area and the maximumweight m_(i) (also referred to as m_(ink)) of the ink ejected per unitsurface area preferably satisfies the condition (m_(i)/30)<M_(u)<m_(i),more preferably satisfies the condition (m_(i)/20)<M_(u)<(m_(i)/3), andmost preferably satisfies the condition (m_(i)/10)<M_(u)<(m_(i)/5). Asused herein, the “maximum weight of the ink ejected per unit surfacearea” refers to the maximum weight per color.

By letting (m_(i)/30)<M_(u), deposition interference can be preventedfrom occurring. Moreover, a high dot size reproducibility can beachieved. By letting M_(u)<m_(i), the ink film can be uniformly formedand a decrease in density can be prevented.

Here, the weight of uncured regions of the undercoating liquid per unitsurface area is determined by a transfer test. Specifically, aftercompletion of the semi-curing step (e.g., after exposure to activeenergy rays) and before deposition of the ink droplets, a permeablemedium such as plain paper is pressed against the undercoating liquidwhich is in a semi-cured state, and the amount of the undercoatingliquid that transfers to the permeable medium is determined by weightmeasurement. The measured value is defined as the weight of the uncuredregions of the undercoating liquid.

For example, if the maximum amount of ink ejected is set to 12picoliters per pixel at a deposition density of 600×600 dpi, the maximumweight m_(i) of the ink ejected per unit surface area becomes 0.04 g/cm²(assuming the density of the ink is about 1.1 g/cm³). Therefore, in thiscase, the weight M_(u) per unit surface area of uncured regions of theundercoating liquid is preferably greater than 0.0013 g/cm² but lessthan 0.04 g/cm², more preferably greater than 0.002 g/cm² but less than0.013 g/cm², and most preferably greater than 0.004 g/cm² but less than0.008 g/cm².

In the practice of the invention, as in the case of the undercoatingliquid, “semi-curing the ink” signifies partial curing, and refers to astate where the liquid ink (i.e., ink, colored liquid) is in a partiallycured, but not a completely cured, state. When the ink liquid ejectedonto the undercoating liquid is semi-cured, the degree of cure may benon-uniform; preferably, the degree of cure proceeds in the depthdirection of the ink liquid. In the present embodiment, the ink that isto be semi-cured is in the form of ink droplets which land on theundercoat or recording medium and form an ink layer.

When this ink is semi-cured and an ink of a different hue is depositedon top of the semi-cured ink, there can be achieved a technical effectwhich is advantageous to the quality of the resulting print. Themechanism of action may be confirmed by examining a cross-section of theprint.

Semi-curing of the ink (i.e., the ink droplets which have landed on therecording medium or the undercoat, or the ink layer formed from inkdroplets which have landed) is explained below.

FIG. 5 is a schematic sectional view of a recording medium where asecond ink d_(b) has been deposited onto a semi-cured first ink d_(a).FIGS. 6A and 6B are schematic sectional views of recording media wheredroplets of the second ink d_(b) have been deposited onto the first inkd_(a) that is in an uncured state, and FIG. 6C is a schematic sectionalview of a recording medium where droplets of the second ink d_(b) havebeen deposited onto the first ink d_(a) that is in a completely curedstate.

When a secondary color is formed by depositing droplets of the secondink d_(b) onto the first ink d_(a) that has been earlier deposited asdroplets, it is preferable to apply the second ink d_(b) onto the firstink d_(a) with the latter in a semi-cured state.

Here, the “semi-cured state” of the first ink d_(a) is similar to theabove-described semi-cured state of the undercoating liquid. As shown inFIG. 5, this is a state where, when the second ink d_(b) is deposited asdroplets onto the first ink d_(a), (1) a portion of the second ink d_(b)emerges at the surface of the first ink d_(a), (2) a portion of thesecond ink d_(b) lies within the first ink d_(a), and (3) the first inkd_(a) is present below the second ink d_(b).

By semi-curing the ink in this way, a cured film (colored film A) of thefirst ink d_(a) and a cured film (colored film B) of the second inkd_(b) can be suitably superimposed, enabling good color reproduction tobe achieved.

By contrast, when the second ink d_(b) is deposited as droplets on thefirst ink d_(a) with the latter in an uncured state, either or both ofthe following occur: all of the second ink d_(b) lies within the firstink d_(a) as shown in FIG. 6A; a state arises where, as shown in FIG.6B, the first ink d_(a) is not present below the second ink d_(b). Inthis case, even when the second ink d_(b) is applied to a high density,the droplets are independent of each other, causing the color saturationof the secondary color to decrease.

When the second ink d_(b) is deposited as droplets on the first inkd_(a) which is completely cured, as shown in FIG. 6C, a state will arisewhere the second ink d_(b) does not lie within the first ink d_(a). Thiscauses interference in the deposition of the droplets to arise, as aresult of which a uniform ink film cannot be formed, leading to adecline in color reproducibility.

Here, when the droplets of the second ink d_(b) are applied to a highdensity, the droplets are not independent of each other. To form auniform film of the second ink d_(b), and also to suppress theoccurrence of deposition interference, the quantity of regions where thefirst ink d_(a) is uncured per unit surface area is preferably smaller,and more preferably substantially smaller, than the maximum quantity ofdroplets of the second ink d_(b) applied thereon per unit surface area.That is, the relationship between the weight M_(da) (also referred to asM_(ink A)) of uncured regions of the first ink d_(a) layer per unitsurface area and the maximum weight m_(db) (also referred to asm_(ink B)) of the second ink d_(b) ejected thereon per unit surface areapreferably satisfies the condition (m_(db)/30)<M_(da)<m_(db), morepreferably satisfies the condition (m_(db)/20)<M_(da)<(M_(db)/3), andmost preferably satisfies the condition (m_(db)/10)<M_(da)<(m_(db)/5).

By letting (m_(db)/30)<M_(da), deposition interference can be preventedfrom occurring. Moreover, a high dot size reproducibility can beachieved. By letting M_(da)<m_(db), a film of the first ink d_(a) can beuniformly formed and a decrease in density can be prevented.

Here, as in the case of the undercoating liquid described above, theweight of the uncured regions of the first ink d_(a) per unit surfacearea is determined by a transfer test. Specifically, after completion ofthe semi-curing step (e.g., after exposure to active energy rays) andbefore deposition of the droplets of the second ink d_(b), a permeablemedium such as plain paper is pressed against the layer of the first inkd_(a) which is in a semi-cured state, and the quantity of the first inkd_(a) that transfers to the permeable medium is determined by weightmeasurement. The measured value is defined as the weight of the uncuredregions of the ink liquid.

For example, if the maximum amount of the second ink d_(b) ejected isset to 12 picoliters per pixel at a deposition density of 600×600 dpi,the maximum weight m_(db) of the second ink d_(b) ejected per unitsurface area becomes 0.04 g/cm² (assuming the density of the second inkd_(b) to be about 1.1 g/cm³). Therefore, in this case, the weight M_(da)per unit surface area of uncured regions of the first ink d_(a) layer ispreferably greater than 0.0013 g/cm² but less than 0.04 g/cm², morepreferably greater than 0.002 g/cm² but less than 0.013 g/cm², and mostpreferably greater than 0.004 g/cm² but less than 0.008 g/cm².

When the semi-cured state of the undercoating liquid and/or the ink isrealized by a polymerization reaction of a polymerizable compound thatis initiated by the irradiation of active energy rays or heating, toenhance the scuff resistance of the print, the unpolymerization ratio(i.e., A_(after polymerization)/A_(before polymerization)) is preferablyat least 0.2 but not more than 0.9, more preferably at least 0.3 but notmore than 0.9, and most preferably at least 0.5 but not more than 0.9.

Here, A_(before polymerization) is the infrared absorption peakabsorbance attributable to polymerizable groups before thepolymerization reaction, and A_(after polymerization) is the infraredabsorption peak absorbance attributable to polymerizable groups afterthe polymerization reaction.

For example, when the polymerizable compound included in theundercoating liquid and/or the ink is an acrylate monomer or amethacrylate monomer, absorption peaks based on polymerizable groups(acrylate groups, methacrylate groups) can be observed near 810 cm⁻¹.Accordingly, the above unpolymerization ratio is preferably defined interms of the absorbances of these peaks. When the polymerizable compoundis an oxetane compound, an absorption peak based on polymerizable groups(oxetane rings) can be observed near 986 cm⁻¹. The aboveunpolymerization ratio is thus preferably defined in terms of theabsorbance of this peak. When the polymerizable compound is an epoxycompound, an absorption peak based on the polymerizable groups (epoxygroups) can be observed near 750 cm⁻¹. Hence, the above unpolymerizationratio is preferably defined in terms of the absorbance of this peak.

A commercial infrared spectrophotometer may be used as the means formeasuring the infrared absorption spectrum. The spectrophotometer may beeither a transmission-type or reflection-type system. Suitable selectionaccording to the form of the sample is preferred. Measurement may becarried out using, for example, an FTS-6000 infrared spectrophotometermanufactured by Bio-Rad.

In the case of a curing reaction based on an ethylenically unsaturatedcompound or a cyclic ether, the unpolymerization ratio may bequantitatively measured from the percent conversion of ethylenicallyunsaturated groups or cyclic ether groups.

The method used to semi-cure the undercoating liquid and/or the ink isexemplified by known thickening methods, e.g., (1) methods that use anagglomerating effect, such as by furnishing a basic compound to anacidic polymer or by furnishing an acidic compound and a metal compoundto a basic polymer; (2) methods wherein the undercoating liquid and/orthe ink is prepared beforehand at a high viscosity, then the viscosityis lowered by adding thereto a low-boiling organic solvent, after whichthe low-boiling organic solvent is evaporated so as to return the liquidto its original high viscosity; (3) methods in which the undercoatingliquid and/or the ink prepared at a high viscosity is first heated, thenis cooled so as to return the liquid to its original high viscosity; and(4) methods in which the undercoating liquid and/or the ink issemi-cured through a curing reaction induced by exposing theundercoating liquid and/or the ink to active energy rays or heat. Ofthese, (4) methods in which the undercoating liquid and/or the ink issemi-cured through a curing reaction induced by exposing theundercoating liquid and/or the ink to active energy rays or heat arepreferred.

“Methods in which the undercoating liquid and/or the ink is semi-curedthrough a curing reaction induced by exposing the undercoating liquidand/or the ink to active energy rays or heat” refers herein to methodsin which the polymerization reaction on polymerizable compounds at thesurface of the undercoating liquid and/or the ink furnished to therecording medium is carried out incompletely. At the surface of theundercoating liquid and/or the ink, compared with the interior thereof,the polymerization reaction tends to be inhibited by the influence ofoxygen present in air. Therefore, by controlling the conditions ofexposure to active energy rays or heat, it is possible to trigger thereaction for semi-curing the undercoating liquid and/or the ink.

The amount of energy required to semi-cure the undercoating liquidand/or the ink varies with the type and content of polymerizationinitiator. When the energy is applied by active energy rays, an amountof about 1 to about 500 mJ/cm² is generally preferred. When the energyis applied as heat, from 0.1 to 1 second of heating under temperatureconditions where the surface temperature of the recording medium fallswithin a temperature range of 40 to 80° C. is preferred.

The application of active energy rays or heat, such as with active raysor heating, promotes the generation of active species by decompositionof the polymerization initiator. At the same time, the increase inactive species or the rise in temperature promotes the curing reactionthrough polymerization or crosslinking of polymerizable or crosslinkablematerials induced by the active species.

A thickening (rise in thickness) may also be suitably carried out byexposure to active rays or by heating.

The ink-jet recording device of the invention is described below infurther detail by referring to the operation of the ink-jet recordingdevice 10, that is, its recording action on the recording medium P.

FIGS. 7A to 7D are views schematically showing steps of forming an imageon a recording medium, respectively.

The recording medium P having been let out from the feed roll 30 istransported in a specified direction (direction “Y” in FIG. 1) byrotation of the transport roll 32 and the transport roller pair 34. Asdescribed above, the recording medium P in this embodiment is a web witha certain length or more and is transported without being cut.

As shown in FIG. 7A, the recording medium P having been let out from thefeed roll 30 comes into contact with the coating roll 60 of theundercoat forming section 13 and the undercoating liquid is applied ontothe surface thereof to form an undercoat U. The drive unit 62 causes thecoating roll 60 to rotate in the direction opposite to the direction oftravel of the recording medium P.

The recording medium P on which the undercoat U has been formed byapplication of the undercoating liquid is further transported by thetransport roll 32 and the transport roller pair 34 of the transportsection 12 and passes through the position facing the undercoatingliquid semi-curing section 14.

As shown in FIG. 7B, the undercoating liquid semi-curing section 14irradiates with ultraviolet light, the recording medium P onto which theundercoating liquid has been applied and which is passing through theposition facing the section 14, thereby semi-curing the undercoat U onthe recording medium P.

The recording medium P having thereon the semi-cured undercoating liquidis further transported by the transport roll 32 and the transport rollerpair 34 of the transport section 12 and passes through the positionfacing the recording head 48X.

The recording head 48X ejects ink droplets from its ejection orifices toform an image on the recording medium P which is being transported bythe transport section 12 and passing through the position opposedthereto.

More specifically, the recording head 48X ejects a first ink droplet d1onto the recording medium P. As shown in FIG. 7C, the first ink dropletd1 ejected from the recording head 48X is deposited onto the surface ofthe undercoat U. The undercoat U is in a semi-cured state and has anuncured surface, and is therefore receptive to the ink droplet d1.

As shown in FIG. 7D, the recording head 48X ejects a second ink dropletd2 in proximity to the position where the previously ejected first inkdroplet d1 was deposited. In this case, the undercoat U is also in asemi-cured state and has an uncured surface, and is therefore receptiveto the ink droplet d2.

In the case where the ink droplets d1 and d2 have been deposited inproximity to each other on the recording medium P, a force acts to makethe ink droplets d1 and d2 coalesce, but interference between the inkdroplets having been deposited onto the recording medium P is suppressedby the resistance force of the undercoat U against coalescence of theink droplets because the undercoat U is semi-cured and has an increasedviscosity.

Ink droplets are thus ejected from the recording head 48X in accordancewith the control by the control unit 20 and deposited onto the recordingmedium P to form an image.

The recording medium P having the image formed by the recording head 48Xis further transported by the transport section 12 and passes throughthe position facing the UV irradiation unit 52X disposed downstream fromthe recording head 48X.

The UV irradiation unit 52X irradiates the recording medium P passingthrough the position opposed thereto with ultraviolet light to semi-curethe image formed by the recording head 48X on the recording medium P,that is, semi-cure the ink droplets having been deposited onto therecording medium P.

Thereafter, the recording medium P is further transported and passes inorder through the positions facing the recording head 48Y, the UVirradiation unit 52Y, the recording head 48C, the UV irradiation unit52C, the recording head 48M, the UV irradiation unit 52M, and therecording head 48K, respectively. As in the case where the recordingmedium P passed through the positions facing the recording head 48X andits corresponding UV irradiation unit 52X, formation of an image andsemi-curing of the formed image are performed each time the recordingmedium P passes through the positions facing the recording head of eachcolor and its corresponding UV irradiation unit.

After an image has been formed by the recording head 48K, the recordingmedium P passes through the position facing the final UV irradiationunit for curing 54.

The final UV irradiation unit for curing 54 irradiates the recordingmedium P with more intense ultraviolet light than the other UVirradiation units to cure the whole of the images on the recordingmedium P formed by the various recording heads including the imagerecorded by the recording head 48K as well as the undercoating liquid.

A color image is thus formed on the recording medium P.

The recording medium P having the color image formed thereon is furthertransported by the transport roll 32 and the transport roller pair 34 tobe taken up onto the recovery roll 36.

The ink-jet recording device 10 thus forms the image on the recordingmedium P.

In the ink-jet recording device 10, the fluorescent lamps 80 of the UVirradiation units 52X, 52Y, 52C and 52M each have the reflective film 90and the phosphor film 92 stacked on top of each other inside the bulb 86with the apertures 94, 96 formed on the recording medium P side, and theapertures 94, 96 have such shapes that the aperture angles α and βsatisfy the conditions: β<α, 60°≦α≦150° and 30°≦β≦90°. Higher intensitylight can be emitted toward the side of the recording medium P, whichensures semi-curing or curing of the undercoating liquid and/or ink onthe recording medium P in a short time, whereby the recording medium Pcan be transported at a higher speed to achieve higher productivity.

Since high intensity light can be selectively emitted toward the side ofthe recording medium P, occurrence of nozzle clogging that may be causedby curing of ink in the ink droplet-ejecting nozzles of the recordingheads under the influence of light the recording heads received from theadjacent fluorescent lamp 80 can be prevented or reduced. In otherwords, stray light on the recording heads can be reduced or eliminatedto prevent or reduce clogging of the ink-jet nozzles, whereby cleaningor replacement of the recording heads is not required or is reduced toachieve higher maintainability, thus enabling images to be consistentlyformed for a long period of time.

Even in the case of an inexpensive fluorescent lamp which is low inemission intensity with respect to the whole periphery of the lamp, therecording medium P can be irradiated with high intensity light in asubstantially uniform manner by providing a reflective film and settingthe aperture angles of the apertures for the reflective film and thephosphor film in the above-defined ranges.

Light from the fluorescent lamp can be thus used efficiently. Therefore,an inexpensive fluorescent lamp can be employed to manufacture theink-jet recording device at a low cost. In addition, fluorescent lampsuse less power than metal halide lamps, high-pressure mercury vaporlamps and other active energy ray-irradiating devices, whereby powerconsumption of the ink-jet recording device can be reduced.

Moreover, high intensity light can be selectively emitted toward therecording medium P side with the use of a fluorescent lamp, whichenables the light intensity and irradiation area to be adjusted withoutrelying on precise reflection design using reflective members or othermembers.

Particularly in the case of semi-curing ink on the recording medium P asin the embodiment under consideration, a considerably large amount ofirradiation excessively or completely cures the ink, whereas a smallamount of irradiation renders the ink uncured. However, according to thepresent invention that is capable of controlling the amount ofirradiation more easily, ink can be reliably semi-cured to a desiredlevel to record a high-resolution image.

By providing the reflective film inside the bulb of the fluorescent lamp(more specifically on the inner wall surface of the bulb), highintensity light can be emitted toward the side of the recording medium Pwithout disposing a reflector or other reflective member on thecircumference of the fluorescent lamp, which avoids the necessity ofleaving space for disposing a reflective member such as a reflector onthe circumference of the fluorescent lamp, thus enabling the UVirradiation units and the image fixing section and hence the ink-jetrecording device to be downsized.

The fluorescent lamp 80 does not emit high intensity light to the areasother than the recording medium P. The housing 82 having the openingformed on the recording medium P side is disposed so as to surround thefluorescent lamp 80, which further ensures that light emitted from thefluorescent lamp 80 reaches the recording medium P while it is preventedfrom being irradiated onto the other areas than the recording medium P.

The cooling mechanism 84 serves to maintain the fluorescent lamp 80 at aconstant temperature, so that the amount of light emitted from thefluorescent lamp 80 is prevented from varying with the temperature andcan be made constant. Ink and/or undercoating liquid can be thusconsistently semi-cured or cured with a constant amount of light.

The cooling mechanism 84 preferably adjusts the surface temperature ofthe fluorescent lamp 80 and more specifically the temperature of itssurface away from the recording medium P in the range of from 30° C. to60° C. and also the temperature variations within 5° C. The amount oflight emitted from the fluorescent lamp 80 can be made constant whileoffering high power by maintaining the temperature within theabove-defined range.

By thus forming the undercoat on the recording medium P, the inkdroplets having been deposited onto the recording medium can beprevented from permeating the recording medium to cause image bleed,thus enabling a high-resolution image to be formed. It also becomespossible to use a recording medium which has a low adhesion to inkdroplets, namely, may repel ink droplets having been depositedthereonto. In other words, image recording on various recording mediabecomes possible. By using the coating roll 60 and, moreover, byrotating the coating roll 60 in a direction opposite to the direction oftravel of the recording medium P to coat undercoating liquid onto therecording medium P, disruption of the surface of the undercoating liquidon the recording medium P when the coating roll 60 separates from therecording medium P after having applied undercoating liquid to therecording medium P can be prevented, enabling the undercoat U having animproved surface state to be formed on the recording medium P.

By semi-curing the undercoat in the undercoating liquid semi-curingsection as in the present embodiment, even when ink droplets havingportions which mutually overlap are deposited on the recording medium,the coalescence of these neighboring ink droplets can be suppressedthrough interactions between the undercoating liquid and the inkdroplets.

That is, by forming a semi-cured undercoat on the recording medium, themigration of ink droplets can be prevented in cases where ink dropletsejected from the recording heads are deposited in close proximity on therecording medium, such as when ink droplets of a single color havingportions which mutually overlap are deposited on a recording medium oreven when ink droplets of different colors having portions whichmutually overlap are deposited on a recording medium.

In this way, image bleed, line width non-uniformities such as of finelines in the image, and color unevenness on colored surfaces can beeffectively prevented from occurring, enabling the formation ofuniform-width, sharp line shapes, and thus making it possible to carryout the recording of ink-jet images of a high deposition density, suchas reversed letters, with good reproducibility of fine features such asfine lines. That is, higher-resolution images can be formed on therecording medium.

By placing a UV irradiation unit between the adjacent recording headsand semi-curing the ink droplets deposited onto (i.e., the image formedon) the recording medium using the respective recording heads, it ispossible to prevent different-color ink droplets deposited at adjacentpositions from overlapping and to keep the deposited ink droplets frommigrating.

On the travel path of the recording medium, the UV irradiation unitcorresponding to the recording head disposed on the furthest downstreamside serves as the final UV irradiation unit for curing and, because itemits higher intensity UV light than the other UV irradiation units, hasthe ability to reliably cure images that have been formed on therecording medium.

In view of further device downsizing, energy saving and cost reduction,the final UV irradiation unit for curing 54 is configured in the samemanner as the UV irradiation units 52X, 52Y, 52C and 52M in theembodiment under consideration. However, use may also be made of variousUV light sources such as metal halide lamps and high-pressure mercuryvapor lamps for the final UV irradiation unit for curing 54.

It is also preferable to use metal halide lamps and high-pressuremercury vapor lamps for the final UV irradiation unit for curing 54. Inother words, the ink-jet recording device is preferably configured sothat the UV irradiation units each including the fluorescent lamp 80 areused for semi-curing the undercoating liquid and/or ink, whereas a metalhalide lamp, high-pressure mercury vapor lamp or other lamp is used forthe final UV irradiation unit for curing 54.

Use of a metal halide lamp, high-pressure mercury vapor lamp or otherlamp for the final UV irradiation unit for curing 54 leads to deviceupsizing but enables higher intensity light to be irradiated onto theundercoating liquid and ink on the recording medium, thus achievingcomplete curing of the undercoating liquid and ink more reliably.

In view of prevention of clogging of the recording head nozzles,production of prints at a high rate, appropriate semi-curing as well asfurther device downsizing, energy saving and cost reduction, it ispreferable for the fluorescent lamp 80 to be provided in every UVirradiation unit for semi-curing the undercoating liquid and/or ink.However, this is not the sole case of the present invention. The ink-jetrecording device may also be configured so that at least one of the UVirradiation units includes the fluorescent lamp 80 and the other UVirradiation units each include a metal halide lamp, a high-pressuremercury vapor lamp, a fluorescent lamp having a reflective film and/or aphosphor film which does not satisfy the above-defined range, or afluorescent lamp having no reflective film.

The fluorescent lamp 80 is preferably disposed at such a position thatthe shortest distance h (mm) between the irradiation surface of thefluorescent lamp 80 and the recording medium P is in the range of from0.5 mm to 1.5 mm. The recording medium P can be irradiated with lightwith high efficiency by disposing the fluorescent lamp 80 at theposition where the above-defined range is satisfied.

In a preferred embodiment, in the case where h is equal to or largerthan 0.5 mm but is smaller than 1.0 mm (0.5≦h<1.0), the housing 82 isdisposed at such a position that the shortest distance H (mm) betweenthe housing 82 and the recording medium P is equal to h (H=h), whereasin the case where h is equal to or larger than 1.0 mm (1.0≦h), thehousing is disposed at such a position that H is equal to 1.0 mm(H=1.0).

The amount of light irradiated onto other portions than the recordingmedium P after having been emitted from the fluorescent lamp 80 can bereduced by disposing the housing 82 at a position satisfying theabove-defined range.

It is preferred to irradiate the recording medium with UV light in aperiod of several hundred milliseconds to 5 seconds after the inkdroplets from the recording head have been deposited on the recordingmedium to thereby semi-cure the ink droplets deposited thereon.

By thus semi-curing the ink droplets in the period of several hundredmilliseconds to 5 seconds after their deposition, the ink droplets onthe recording medium can be prevented from getting out of shape,enabling a high-resolution image to be formed.

The undercoating liquid has a viscosity of preferably at least 10 mPa·sbut not more than 500 mPa·s, and more preferably at least 50 mPa·s butnot more than 300 mPa·s.

At an undercoating liquid viscosity of at least 10 mPa·s, and morepreferably at least 50 mPa·s, as noted above, it is possible to coat theundercoating liquid onto even a recording medium to which liquid doesnot readily adhere.

At an undercoating liquid viscosity of not more than 500 mPa·s, and morepreferably not more than 300 mPa·s, it is possible to more reliablyachieve a lower surface roughness in the undercoat that is formed on therecording medium P.

The ink-jet recording device 10 is described below in further detailwith reference to specific examples.

In the example to be described below, measurement was made for the printproductivity and the state of clogging of the recording head nozzles bysetting the aperture angle α of the aperture 94 for the reflective film90 of the fluorescent lamp 80 and the aperture angle β of the aperture96 for the phosphor film 92 of the fluorescent lamp 80 to variousvalues.

A linear tube with a diameter of 32 mm was used for the bulb and aphosphor emitting light at a central wavelength of 365 nm was used forthe phosphor film in the fluorescent lamp 80.

The fluorescent lamp 80 was disposed at such a position that theshortest distance h between the irradiation surface of the fluorescentlamp and the recording medium P was 1 mm, whereas the housing 82 wasdisposed at such a position that the shortest distance H between thehousing 82 and the recording medium P was 1 mm. The ink-jet head usedwas one having a resolution of 600 dpi.

Measurement was made under the above-described conditions usingfluorescent lamps each of which included the reflective film 90 whoseaperture 94 had an aperture angle α of 210°, 180°, 170°, 150°, 120°,91°, 60°, or 30° while also changing the aperture 96 in the phosphorfilm 92 so as to have an aperture angle β of 180°, 120°, 90°, 60°, or30° in the above respective cases.

Measurement was made for the productivity according to the methoddescribed below.

About 12 pl of ink droplets were ejected from the recording head ontothe semi-cured undercoat with a thickness of 5 μm formed on therecording medium P at a density of 600×600 dpi to thereby form aso-called solid image. Then, UV light was irradiated onto the solidimage from the UV irradiation unit having the fluorescent lampsatisfying the respective conditions described above. Whether or not thedeposited ink droplets had been semi-cured following passage of therecording medium under the UV irradiation unit was checked.

Whether or not the ink droplets had been semi-cured was checked for therecording media P transported at various transport speeds. Of thetransport speeds at which the ink droplets were found to be semi-cured,the fastest transport speed was regarded as the speed appropriate forthe productivity.

Next, recording operation was continuously made for 1 hour, then therecording head was wiped off. Thereafter, whether or not the recordinghead nozzles were clogged was checked from the state of ejection fromthe recording head nozzles. More specifically, the recording headfollowing wiping off was rated “excellent” when the state ofnon-ejection was not found in any nozzle, “good” when some of thenozzles were in the state of non-ejection but could be recovered with asimple maintenance operation, “fair” when some of the nozzles were inthe state of non-ejection but could be recovered with a usualmaintenance operation, and “poor” when some of the nozzles were in thestate of non-ejection and could not be recovered thus requiringreplacement with a new recording head.

The evaluation results are shown in Table 1 below.

TABLE 1 Aperture angle Aperture Productivity α in reflective angle β in(high-speed Nozzle Evalu- film phosphor film performance) clogging ation210 ° 180° 100 mm/s Poor Poor 120° 200 mm/s Poor Poor  90° 300 mm/s PoorPoor  60° 400 mm/s Poor Poor  30° 300 mm/s Poor Poor 180° 180° 100 mm/sPoor Poor 120° 200 mm/s Poor Poor  90° 300 mm/s Poor Poor  50° 400 mm/sPoor Poor  30° 300 mm/s Poor Poor 170° 180° 100 mm/s Poor Poor 120° 200mm/s Poor Poor  90° 300 mm/s Poor Poor  60° 400 mm/s Poor Poor  30° 300mm/s Poor Poor 150° 180° 100 mm/s Fair Poor 120° 200 mm/s Fair Poor  90°400 mm/s Eair Fair  60° 600 mm/s Fair Fair  30° 400 mm/s Fair Fair 120°180° 100 mm/s Good Poor 120° 200 mm/s Good Poor  90° 400 mm/s Good Good 60° 600 mm/s Good Good  30° 400 mm/s Good Good  90° 180° 100 mm/s GoodPoor 120° 200 mm/s Good Poor  90° 300 mm/s Good Poor  60° 600 mm/s GoodGood  30° 400 mm/s Good Good  60° 180° 100 mm/s Excellent Poor 120° 200mm/s Excellent Poor  90° 200 mm/s Excellent Poor  60° 300 mm/s ExcellentPoor  30° 400 mm/s Excellent Excellent  30° 180°  50 mm/s Excellent Poor120°  50 mm/s Excellent Poor  90° 100 mm/s Excellent Poor  60° 200 mm/sExcellent Poor  30° 200 mm/s Excellent Poor

Table 1 shows that nozzle clogging can be suppressed by adjusting theaperture angle α of the aperture for the reflective film to not morethan 150°; can be further suppressed at an aperture angle α of not morethan 120°, enabling the nozzles to be recovered with a simplemaintenance operation; and can be prevented at an aperture angle α ofnot more than 60°.

It is also seen that, by setting the aperture angle α of the aperturefor the reflective film and the aperture angle β of the aperture for thephosphor film so as to satisfy the conditions: β<α, 60°≦α≦150° and30°≦β≦90°, ink droplets can be semi-cured even at a recording medium Ptransport speed of 400 mm/s while also suppressing nozzle clogging,whereby high-resolution images can be consistently and rapidly producedfor a long period of time.

The above results clearly show the beneficial effects of the presentinvention.

The reflective film of the fluorescent lamp 80 preferably has atransmittance of not more than 10%.

At a reflective film transmittance of not more than 10%, light is morereliably prevented from being emitted from the other areas than theapertures, whereby the recording medium P can be irradiated with higherintensity light to achieve further improved productivity. UV light isalso more reliably prevented from reaching the recording heads.

The various effects as described above can be achieved by providing thefluorescent lamp with such a shape that the aperture angle α of theaperture for the reflective film and the aperture angle β of theaperture for the phosphor film satisfy β<α, 60°≦α≦150° and 30°≦β≦90°.However, irrespective of the aperture shapes in the phosphor film andthe reflective film, curing in a shorter period of time is possible bysetting the transmittance of the reflective film in the fluorescent lampto not more than 10%. The transport speed of the recording medium andhence the productivity can be improved.

A further detailed description is given below with reference to anotherspecific example.

An ink-jet recording device of the same structure as in the firstexample was used in this example, and the print productivity wasmeasured using four fluorescent lamps in which the reflective films hadtransmittance values of 30%, 20%, 10% and 5%, respectively. In thisexample, the aperture in the reflective film had an aperture angle of90°, whereas the aperture in the phosphor film had an aperture angle of60°.

The measurement results are shown in Table 2 below.

TABLE 2 Transmittance of reflective Productivity (high-speed filmperformance) 30%  50 mm/s 20% 100 mm/s 10% 400 mm/s  5% 600 mm/s

As is seen from Table 2, the productivity can be drastically improved bysetting the reflective film transmittance to not more than 10%. It isclear that a similar tendency is seen even if the aperture angle ischanged.

The above results clearly show the beneficial effects of the presentinvention.

As in the above-described embodiment, the aperture for the reflectivefilm and that for the phosphor film in the fluorescent lamp preferablyhave shapes which are symmetric with respect to the axial planeconnecting the center of the fluorescent lamp (i.e., axis of the tubularmember) with the recording medium.

By thus forming the apertures for the reflective film and the phosphorfilm so as to have symmetric shapes with respect to the axial planeconnecting the center of the fluorescent lamp with the recording medium,light emitted from the fluorescent lamp can be irradiated onto therecording medium which is at the shortest distance from the fluorescentlamp, while also reducing the area where light emitted from thefluorescent lamp is irradiated. In this way, the recording medium can beirradiated with higher intensity light. In addition, light is morereliably prevented from reaching the adjacent recording heads to causetheir nozzles to be clogged.

A getter is preferably sealed within the fluorescent lamp.

The getter included therein can prolong the service life of thefluorescent lamp. In other words, the intensity of light emitted fromthe fluorescent lamp can be maintained for a long time to enable thereplacement frequency and the running costs to be reduced.

Use of a zirconium alloy for the getter enables the getter to initiate agas adsorption reaction more easily.

In the above-described embodiment, the cooling mechanism is provided inthe housing, but the present invention is not limited to this as long asthe fluorescent lamp can be cooled. In the case of a structure in whichthe UV irradiation unit has no housing, a cooling mechanism may beseparately disposed.

It is preferable to provide a cooling mechanism that cools thefluorescent lamp and keeps the temperature of the fluorescent lampconstant, because light can be more consistently emitted from thefluorescent lamp. However, this is not the sole case of the presentinvention and the fluorescent lamp may not be provided with a coolingmechanism.

In the present embodiment, by disposing UV irradiation units betweenrecording heads of the respective ink colors and curing the image areason the recording medium each time an image is recorded at each of therespective recording heads, as noted above, it is possible to preventink of different colors from intermingling, thus enabling higherresolution images to be formed. Accordingly, a UV irradiation unit waspositioned at each of the recording heads. However, the presentinvention is not limited in this regard. To illustrate, in analternative arrangement, a single UV irradiation unit may be disposedfor a plurality of recording heads.

In the present embodiment, the recording head unit has recording headsof a total of five colors consisting of a special color (X) and yellow(Y), cyan (C), magenta (M) and black (K). However, it is also possibleto employ a recording head unit having other combinations of heads,including a recording head unit having heads for only the four colorsYCMK, or a recording head unit having heads for six or more colors,including another special color head. The recording heads of therespective colors may be disposed in any order without any particularlimitation.

Nor is the invention limited to requiring the disposition of a pluralityof recording heads. That is, the ink-jet recording device of theinvention may be one which uses a single recording head to form an imageon the recording medium, then irradiates the image with UV light to forma single-color image.

The digital label printer using the ink-jet recording device of theinvention is described below.

FIG. 8 is a front view showing, in simplified form, a digital labelprinter which uses an ink-jet recording device according to theinvention, and FIG. 9 is a longitudinal sectional view of a recordingmedium P for printing labels such as may be used in the digital labelprinter shown in FIG. 8.

A digital label printer in the present embodiment records an image ontoa web-type recording medium for printing labels at an image formingsection, then makes label-shaped slits in the medium P with a die cutterin a post-treatment section. In addition, the printer carries out, as asubsequent step, a waste removal operation in which unnecessary portionsof the pressure-sensitive adhesive sheet are peeled from the backingsheet (peel sheet) and removed.

In the example described below, an active ray curing-type digital labelprinter which uses a UV-curable ink as the active ray-curable ink thatcures upon exposure to active rays is described by way of illustration.However, the invention is not limited in this regard, and may be appliedto digital label printers which use any of various kinds of activeray-curable inks, as well as to any other type of digital label printer.

Referring to FIG. 9, a web-type recording medium P for printing labels(also referred to below as simply “recording medium P”) used in thepresent embodiment has a two-layer construction composed of a peel sheet182 as a backing sheet on which is laminated a pressure-sensitiveadhesive sheet 180 coated on the back side thereof with apressure-sensitive adhesive 180 a.

As shown in FIG. 8, a digital label printer 100 has a transport section110; an undercoat forming section 13; an undercoating liquid semi-curingsection 14; an image forming section 112 including an image recordingsection 16 and an image fixing section 18; a post-treatment section 114;and a control unit 116.

Here, the transport section 110 transports the web-type recording mediumP for printing labels in a fixed direction (from left to right in FIG.8). The image forming section 112 and the post-treatment section 114 arearranged in this order in the direction of travel of the recordingmedium P; that is, in the upstream to downstream direction, morespecifically in the order of the undercoat forming section 13, theundercoating liquid semi-curing section 14, the image forming section112 and the post-treatment section 114. Although partially not shown inFIG. 8, the control unit 116 is connected to the undercoat formingsection 13, the undercoating liquid semi-curing section 14, thetransport section 110, the image forming section 112 and thepost-treatment section 114, and controls their respective operations.

The transport section 110 has a feed roll 30, a transport roll 32,transport roller pairs 126, 128, 130 and 132, a product roll 134, andtransport motors 128 a and 134 a.

The feed roll 30 has the web-type recording medium P for printing labelswound thereon in the form of a roll.

The transport roll 32 and the transport roller pairs 126, 128, 130 and132 are arranged in this order from the upstream to the downstream sideof the travel path of the recording medium P. The transport roll 32 andthe transport roller pairs 126, 128, 130 and 132 let out the recordingmedium P from the feed roll 30, and transport the recording medium P ina given direction (in the present embodiment, from left to right in FIG.8).

As in the ink-jet recording device 10 described above, the transportroll 32 changes the travel path of the recording medium P from theobliquely upward direction to the horizontal direction.

The product roll 134, which is disposed the furthest downstream on therecording medium P travel path, i.e., in the direction of transport,takes up the recording medium P that has been transported over thetravel path by the transport roll 32 and the transport roller pairs 126,128, 130 and 132 and has passed through the undercoat forming section13, the undercoating liquid semi-curing section 14, the image formingsection 112, and the post-treatment section 114.

The transport motors 128 a and 134 a are connected to, respectively, thetransport roller pair 128 and the product roll 134, and rotatably drivethe transport roller pair 128 and the product roll 134.

That is, in the present embodiment, the transport roller pair 128 andthe product roll 134 connected to the transport motors 128 a and 134 a,respectively, are driven to rotate and thus serve as the drive rollersfor transporting the recording medium P. The other transport rollerpairs 126, 130 and 132 and the transport roll 32 are driven rollerswhich rotate with movement of the recording medium P and regulate therecording medium P on the travel path.

In the transport section 110, the transport motors 128 a and 134 arotatably drive the transport roller pair 128 and the product roll 134.Through this arrangement, the recording medium P is let out from thefeed roll 30, passes through the undercoat forming section 13, theundercoating liquid semi-curing section 14, the image forming section112, and the post-treatment section 114, and is taken up onto theproduct roll 134.

In the present embodiment, a transport buffer is provided between theimage forming section 112 and the post-treatment section 114.

By providing such a transport buffer, it is possible to absorb slackthat arises in a web-type recording medium P for printing labels due toa difference between the transport speed in the image forming section112 and that in the post-treatment section 114, thus enabling the labelsto be efficiently produced.

The transport motors 128 a and 134 a are connected to a subsequentlydescribed transport motor controller and their rotational speeds therebycontrolled. This in turn controls the speed at which the web-typerecording medium P for printing labels is transported by the transportsection 110.

No particular limitation is imposed on the transport roller pairs whichfunction as drive roller pairs. For example, transport motors may beprovided for all the transport roller pairs so that all the transportroller pairs function as drive roller pairs.

As described above, the undercoat forming section 13 includes a coatingroll 60, a drive unit 62, a reservoir 64, a scraper roll 66, a driveunit 67 and a positioning unit 68. The arrangement and function of eachelement of the undercoat forming section 13 are the same as those in theundercoat forming section 13 of the ink-jet recording device 10 asdescribed above, and therefore their detailed description is omitted.

The coating roll 60 of the undercoat forming section 13 contacts therecording medium P as it is rotated in the direction opposite to thedirection of travel of the recording medium P, whereby the undercoatingliquid is applied onto the surface of the recording medium P.

The undercoat is thus formed on the surface of the recording medium P.

The undercoating liquid semi-curing section 14 is disposed on thedownstream side of the undercoat forming section 13 in the direction oftravel of the recording medium P. The layout and function of theundercoating liquid semi-curing section 14 in this embodiment are thesame as those of the undercoating liquid semi-curing section 14 of theink-jet recording device 10 described above and therefore their detaileddescription is omitted here.

The undercoating liquid semi-curing section 14 semi-cures the undercoatby irradiating with ultraviolet light the recording medium P which hasthe undercoat formed thereon through application of the undercoatingliquid and which is transported by the transport section 110 to passthrough the position opposed thereto.

The image forming section 112 includes the image recording section 16and the image fixing section 18.

The image recording section 16 and the image fixing section 18 areconfigured in the same manner as the image recording section 16 and theimage fixing section 18 of the ink-jet recording device 10 shown in FIG.1 and therefore their detailed description is omitted.

The image recording section 16 includes a recording head unit 46 havingrecording heads 48X, 48Y, 48C, 48M and 48K, and the image fixing section18 includes four UV irradiation units 52X, 52Y, 52C and 52M and a finalUV irradiation unit for curing 54.

As above, the recording heads 48X, 48Y, 48C, 48M and 48K as well as theUV irradiation units 52X, 52Y, 52C, 52M and 54 are arranged, from theupstream to the downstream side in the direction of travel of therecording medium P, in the following order: recording head 48X, UVirradiation unit 52X, recording head 48Y, UV irradiation unit 52Y,recording head 48C, UV irradiation unit 52C, recording head 48M, UVirradiation unit 52M, recording head 48K and final UV irradiation unitfor curing 54.

The image forming section 112 ejects ink droplets from each of therecording heads, then cures the ink droplets on the recording medium Pby applying UV light from each of the UV irradiation units 52X, 52Y,52C, 52M and 54, thereby forming an image.

The post-treatment section 114 is disposed on, in the recording medium Ptravel direction, the downstream side of the UV irradiation unit 54corresponding to the recording head 48K. It has a varnish coater 162 andan UV irradiator 164 for coating the image surface with a clear, activeray-curable liquid (in the present embodiment, a clear, UV-curableliquid) and improving the gloss, a die cutter 166 for makinglabel-shaped slits in the web-type recording medium P, and a waste roll172 for peeling off unnecessary portions of the recording medium P.

As described above, the transport buffer is provided between the UVirradiation unit 54 corresponding to the recording head 48K and thevarnish coater 162.

The varnish coater 162 is a clear liquid feeding means which feedsactive ray- (in this embodiment, ultraviolet light-) curable clearliquid (referred to below as “active ray-curable clear liquid” or simply“clear liquid”) to the surface of the recording medium P, and which issituated on the downstream side, in the travel direction of therecording medium P, of the UV irradiation unit 54 corresponding to therecording head 48K.

The varnish coater 162 has a pair of coating rolls to the surface ofwhich adheres (on which has been impregnated) a UV-curable clear liquid,and which rotate in accordance (synchronous) with movement of therecording medium P while nipping the recording medium P, thereby coatingthe surface of the foil-stamped recording medium P (the side on which animage has been formed) with the UV-curable clear liquid.

Here, the clear liquid coated by the varnish coater 162 is an activeray-curable clear liquid which can be cured by exposure to ultravioletlight. Exemplary clear liquids include cationic-polymerizablecompositions, radical-polymerizable compositions and aqueouscompositions which contain as the primary ingredients at least apolymerizable compound and a photoinitiator. The clear liquid isdescribed in detail later in the specification.

The UV irradiator 164 is disposed on the downstream side of the varnishcoater 162 in the travel direction of the recording medium P. The UVirradiator 164 irradiates the surface of the recording medium P withactive rays (in this embodiment, ultraviolet light), thereby curing theUV-curable clear liquid that has been coated onto the surface of therecording medium P. The UV irradiator 164 may also adopt various layoutssuch as the one shown in the UV irradiation units 52X, 52Y, 52C, 52M and54 described above.

The UV-curable clear liquid is coated onto the surface of the recordingmedium P and cured, enabling luster to be imparted to the image side ofthe recording medium P and making it possible to improve the imagequality.

The die cutter 166 makes slits 180 b of a desired label shape in onlythe pressure-sensitive adhesive sheet 180 of a printed, web-typerecording medium P for printing labels, as shown in FIG. 9. The diecutter 166 is situated on the downstream side of the UV irradiator 164in the travel direction of the recording medium P, and has a cylindercutter 168 disposed on the image-forming side of the recording medium Pand an anvil roller 170 disposed on the opposite side of the recordingmedium P from the cylinder cutter 168.

The cylinder cutter 168 is composed of a cylinder 168 a and a pluralityof slitting blades 168 b which are wound around the cylindrical surfaceof the cylinder 168 a and are formed according to the shape andarrangement of the labels.

The die cutter 166 preferably undergoes an intermittently rockingmotion, that is, adjusts the rotational speed and rotational directionto form slits in the pressure-sensitive adhesive sheet 180.

The die cutter 166, while nipping the recording medium P between thecylinder cutter 168 and the anvil roller 170, undergoes anintermittently rocking rotation which is synchronous with the transportspeed of the recording medium P, causing the slitting blades 168 b tomake label-shaped slits in only the pressure-sensitive adhesive sheet180 of the recording medium P, thus producing labels in the recordingmedium with high efficiency.

The waste roll 172 peels from the peel sheet 182 and takes upunnecessary portions (label borders) of the pressure-sensitive adhesivesheet 180 which do not form labels (finished product) L.

The thus taken up recording medium P after unnecessary portions havebeen peeled, that is, the recording medium P in a state where only thelabels L remain adhering to the peel sheet 182, is then taken up ontothe product roll 134, giving the final product.

The control unit 116 has a memory which stores recording image data forink ejection from the recording heads 48X, 48Y, 48C, 48M and 48K of therecording head unit 46, a head drive controller for controlling thedrive of the recording heads 48X, 48Y, 48C, 48M and 48K of the recordinghead unit 46 based on the recording image data, an image data analyzerfor analyzing the shapes of the labels L based on the image data storedin the memory, a transport speed changer for changing the transportspeed of the web-type recording medium P for printing labels based onthe shapes of the labels L analyzed by the image data analyzer, thetransport motor controller for controlling the rotational speed of thetransport motors 128 a and 134 a based on the transport speed changed bythe transport speed changer, and a die cutter controller for controllingthe rotational speed of the die cutter 166 based on the transport speedchanged by the transport speed changer. The control unit 116 adjusts thetiming at which ink droplets are ejected from each recording head, theamount of ejection, the speed at which the recording medium istransported by the transport section 110, and the timing at which therecording medium is cut with the die cutter.

Next, a method for producing labels with the digital label printer 100is described.

Referring to FIG. 8, the recording medium P that has been let out fromthe feed roll 30 onto which it is wound into a roll is transported bythe transport section 110 to the image forming section 112 after theundercoating liquid has been applied with the coating roll 60 of theundercoat forming section 13 and the undercoat has been semi-cured inthe undercoating liquid semi-curing section 14.

The recording medium P transported to the image forming section 112passes through the positions opposite the recording heads 48X, 48Y, 48C,48M and 48K.

The recording heads 48X, 48Y, 48C, 48M and 48K eject, under control bythe control unit 116, droplets of UV-curable ink onto the recordingmedium P passing through positions opposed thereto. The recording mediumP onto which the ink has been ejected then travels further and passesthrough positions opposite the corresponding UV irradiation units 52X,52Y, 52C, 52M and 54, where it is irradiated with ultraviolet light,thereby curing the ink.

That is, when the recording medium P passes through positions oppositethe recording heads 48X, 48Y, 48C, 48M and 48K, ink droplets are ejectedonto the recording medium P from the recording heads 48X, 48Y, 48C, 48Mand 48K. The recording medium P is subsequently exposed to ultravioletlight from the UV irradiation units 52X, 52Y, 52C, 52M, causing the inkto cure. After the image formation with the recording head 48K,ultraviolet light is emitted from the final UV irradiation unit forcuring 54 to ensure curing of the various inks and undercoating liquid.An image is thus formed on the surface of the recording medium P.

The recording medium P on which images have been formed is transportedthrough the transport buffer to the post-treatment section 114, where aUV-curable clear liquid is applied by the varnish coater 162 to thesurface of the recording medium P, then is cured by the UV irradiator164.

The recording medium P that has been coated with the UV-curable clearliquid is transported to the die cutter 166, where slits 180 b in theshape of labels L are made only in the pressure-sensitive adhesive sheet180 by means of the cylinder cutter 168 and the anvil roller 170.

At this time, because the die cutter 166, as noted above, makes slits180 b in the shape of labels L while intermittently rocking, the slits180 b can be continuously formed. Waste from the recording medium P canthus be minimized.

Unnecessary portions (portions other than the labels L) of thepressure-sensitive adhesive sheet 180 of the recording medium P arepeeled from the peel sheet 182 and taken up onto the waste roll 172. Therecording medium P on which only the labels L remain affixed to the peelsheet 182 is taken up onto the product roll 134, thereby giving a finalproduct.

Labels are produced by the procedure described above.

In this way, use of the above-described various fluorescent lamps forthe fluorescent lamps of the UV irradiation units enables the digitallabel printer 100 as well to semi-cure or cure the inks and theundercoating liquid in a short period of time without relying on anexpensive, high-power fluorescent lamp, thus achieving a higherproduction rate. Nozzle clogging is also prevented from occurring in therecording heads of the image forming section. Therefore, high-resolutionand high-quality labels can be consistently and rapidly produced for along period of time.

Moreover, the digital label printer 100 of the present embodimentcarries out peel processing in which the transport speed changer, basedon label shape data, slows the transport speed of the recording medium Pat positions of label portions which are vulnerable to the peeling ofunnecessary portions, thereby preventing the breakage or rupture of thelabels L during post-treatment (waste removal) and enabling the reliableremoval of unnecessary portions other than the label portions. In thisway, halting of the apparatus due to the breakage or rupture of labels Lis eliminated, enhancing productivity and making it possible toinexpensively provide labels L.

In the present embodiment, label-shaped slits are made with the diecutter in the post-treatment section, but the die cutter may be replacedby a laser cutter to make slits 180 b of a desired label shape in onlythe pressure-sensitive adhesive sheet 180 of a printed, web-typerecording medium P for printing labels.

The undercoat forming section 13 integrated with the image formingsection 112 and the post-treatment section 114 may be provided in thedigital label printer as independent and discrete apparatuses. In otherwords, the digital label printer may include a front-end processing unithaving an undercoat forming section and an image forming section and aback-end processing unit having a post-treatment section and be operatedas follows: An image is formed on the recording medium in the front-endprocessing unit, after which the recording medium is taken up; then, therecording medium having the image formed thereon is set on the back-endprocessing unit, where slits are made in the recording medium andunnecessary portions are taken up to obtain a product.

Next, use may be made of various recording media, undercoating liquidsand inks in the ink-jet recording device of the present invention.

The recording medium used in the ink-jet recording device of the presentinvention may be a permeable recording medium, an impermeable recordingmedium or a slowly permeable recording medium.

Illustrative examples of permeable recording media include plain paper,porous paper, and other recording media capable of absorbing liquids.Illustrative examples of impermeable or slowly permeable recording mediainclude art paper, synthetic resin, rubber, resin-coated paper, glass,metal, ceramic and wood. In the practice of the invention, compositerecording media in which a plurality of these materials are combined mayalso be used for the purpose of adding the functionality thereof.

The ink, which has at least a composition suitable for forming images,includes at least one polymerizable or crosslinkable material, andoptionally includes as well a polymerization initiator, a hydrophilicsolvent, a colorant and other ingredients. Use may be made of one thatcures upon exposure to active energy rays.

The undercoating liquid includes at least one polymerizable orcrosslinkable material, and optionally includes as well a polymerizationinitiator, a hydrophilic solvent, a colorant and other ingredients. Itis preferable for the undercoating liquid to be formulated so as to havea different composition than the ink.

The polymerization initiator is a compound which is capable ofinitiating a polymerization reaction or crosslinking reaction under theinfluence of active energy rays. An undercoating liquid that has beenapplied to the recording medium can in this way be cured by exposure toactive energy rays.

The undercoating liquid preferably includes a radical-polymerizablecomposition. As used herein, “radical-polymerizable composition” refersto a composition which includes at least one radical-polymerizablematerial and at least one radical polymerization initiator. Because theundercoating liquid includes a radical-polymerizable composition, theundercoating liquid curing reaction can be carried out at a highsensitivity in a short period of time.

Moreover, it is preferable for the ink to include a colorant. It ispreferable for the undercoating liquid which is used in combination withthis ink to either have a composition that includes no colorant orincludes less than 1 wt % of colorant, or to have a composition thatincludes a white pigment as the colorant.

Although the ink-jet recording device of the present invention has beendescribed above in detail, it should be noted that the present inventionis by no means limited to the foregoing embodiments and variousimprovements and modifications can be made without departing from thespirit and scope of the present invention.

For example, a phosphor emitting UV light is used for the phosphor filmin the above-described embodiment, because the device can bemanufactured at a lower cost and UV-curable inks and undercoating liquidare used. However, this is not the sole case of the present inventionand the phosphor used may be one that emits light having such awavelength that an active energy ray-curable ink and/or undercoatingliquid used as the ink and/or undercoating liquid cures.

Because a higher-resolution image can be recorded, the ink-jet recordingdevice in the above-described embodiment is provided with the undercoatforming section to form an undercoat on the recording medium beforeforming an image thereon. However, an image may be directly formed onthe recording medium having no undercoat formed thereon withoutproviding the ink-jet recording device with the undercoat formingsection.

1. An ink-jet recording device comprising: transport means fortransporting a recording medium; image forming means which includes atleast one ink-jet head that ejects, based on image signals, inkcontaining at least a colorant and cured by exposure to active energyrays onto said recording medium transported by said transport means andmoved to a position opposed to said at least one ink-jet head; and imagecuring means which includes at least one light irradiation unit having afluorescent lamp from which the active energy rays are emitted, andwhich cures the ink deposited on said recording medium by irradiation ofan image formed on said recording medium with the active energy raysfrom said at least one light irradiation unit, wherein said fluorescentlamp has a bulb, a reflective film formed on a large part of an innerwall of said bulb and having a first aperture formed on a side of saidrecording medium, and a phosphor film formed on said reflective film anda part of said inner wall of said bulb and having a second apertureformed on the side of said recording medium, and wherein formulas: β<α,60°≦α≦150° and 30°≦β≦90° where α represents a first aperture angle ofsaid first aperture for said reflective film and β represents a secondaperture angle of said second aperture for the phosphor film, aresatisfied.
 2. The ink-jet recording device according to claim 1, whereinsaid reflective film has a transmittance of not more than 10%.
 3. Anink-jet recording device comprising: transport means for transporting arecording medium; image forming means which includes at least oneink-jet head that ejects, based on image signals, ink containing atleast a colorant and cured by exposure to active energy rays onto saidrecording medium transported by said transport means and moved to aposition opposed to said at least one ink-jet head; and image curingmeans which includes at least one light irradiation unit having afluorescent lamp from which the active energy rays are emitted, andwhich cures the ink deposited on said recording medium by irradiation ofan image formed on said recording medium with the active energy raysfrom said at least one light irradiation unit, wherein said fluorescentlamp has a bulb, a reflective film formed on a large part of an innerwall of said bulb and having a first aperture formed on a side of therecording medium, and a phosphor film formed on said reflective film anda part of said inner wall of said bulb and having a second apertureformed on the side of said recording medium, and wherein said reflectivefilm has a transmittance of not more than 10%.
 4. The ink-jet recordingdevice according to claim 1, wherein said first aperture of saidreflective film and said second aperture of said phosphor film aresymmetric with respect to a axial plane connecting a centre of saidfluorescent lamp with said recording medium.
 5. The ink-jet recordingdevice according to claim 1, wherein said at least one light irradiationunit further includes a housing which is disposed so as to surround saidfluorescent lamp and has an opening formed on the side of said recordingmedium.
 6. The ink-jet recording device according to claim 1, whereinsaid at least one ink-jet head is of a full-line type in which said atleast one ink-jet head has a length in a direction perpendicular to adirection of travel of said recording medium which is larger than awidth of said recording medium and ink droplets can be ejected over awhole area of said recording medium in the direction perpendicular tothe direction of travel of said recording medium.
 7. The ink-jetrecording device according to claim 1, wherein said at least one ink-jethead of said image forming means comprises at least two ink-jet headsfrom which inks of different colors are ejected, and wherein said atleast one light irradiation unit of said image curing means comprises atleast one light irradiator disposed between adjacent ink-jet heads ofsaid at least two ink-jet heads in a direction of travel of saidrecording medium and a final light irradiator which irradiates theactive energy rays onto images formed on said recording medium.
 8. Theink-jet recording device according to claim 7, wherein said final lightirradiator is configured as in said at least one light irradiator. 9.The ink-jet recording device according to claim 7, wherein said finallight irradiator comprises a metal halide lamp or a high-pressuremercury vapor lamp.
 10. The ink-jet recording device according to claim7, wherein said at least one light irradiator disposed between saidadjacent ink-jet heads of said at least two ink-jet heads semi-cures inkconstituting an image formed by an ink-jet head located upstream of saidat least one light irradiator in the direction of travel of saidrecording medium, and wherein said final light irradiator cures inks ofthe images formed on said recording medium.
 11. The ink-jet recordingdevice according to claim 1, further comprising: undercoating liquidapplying means which is disposed upstream from said image forming meansin a direction of travel of said recording medium transported by saidtransport means and which applies to said recording medium undercoatingliquid that cures upon exposure to the active energy rays; andundercoating liquid semi-curing means which is disposed downstream ofsaid undercoating liquid applying means in the direction of travel ofsaid recording medium and which includes a light irradiation unit, saidundercoating liquid applied onto said recording medium being irradiatedwith active energy rays from said light irradiation unit to semi-curesaid undercoating liquid applied on said recording medium.